Brake



L. C. HUCK Nov. 8, 1932.

BRAKE Filed June 30, 1930 @QZ (pa:

lA nl Patented Nov., 1932 LOUIS C. BUCK, 0F NEW YOBK,'N. Y.

BRAKE I Application med June 80,1930. i Serial No. 464,851.

This invention relates to brakes, more especially to internal shoe brakes as used quite generally on motor vehicles.

One object of the invention is to secure maximum braking eiliciency with yminimum pedal pressure.

Another object ings having relatively high coeicients of friction. v.

Another object is to so designthe brake as to leave as much of the drum surface as possible free from engagement by the shoes to permit the use of another similar or dissimilar brake within the same drum.

Another object is to secure an automatic change in the distribution of the pressures along the arc of the shoe between the shoe and the drum surface so as to avoid unduly high pedal pressure under certain conditions,

and grabbing of the shoe under other conditions.

Many other advantages will be understood from the description.

' Fig. 1 is a view of the brake showing the parts in side elevation. p Fig. 2 is a diagrammatic view to illustrate the shifting high pressure positions.

Fig. detail. Fig. 4v is a section on line 4-4 of Fig. 1.

The brake is shown as comprising two shoes, a long shoe 7 and a short shoe 9. These shoes are shown in a position to be expanded Vby a cam 11 located between their adjacent ends. The shoes'frictionallyengag'e is also a diagrammatic view of a the ange ofa drum 13 which preferably,

and in motor vehicle practice,'will be carrieduby a vclliclewheel. The direction of drum rotation shown VbyY the arrow-represrnts the direction of rotation for forward vehicle travel. It will be seen that thelong shoe 7 becom'es self-actuating for the direction of rotation of the drum indicated. The short shoe is directly pivoted Lbya pivot pin 15 to the fixed plate 17. On the other hanl a link 18 is-pivoted at 19`to-the long shoe and at 21 to the fired plate'17. Preferably the 'cam is arranged to actuate the shoes by links or roller sectors. 29 pivoted adjacent the ends of. theshoes-as at 31. Ifound is to permit the use of linnecessary any convenient means such, for, example, as a pin and slot between the eX- treme end of the shoes and the links 29 may be employed to limit the movement `of the link about its pivot 31. Such a construction constitutes no partv of the invention herein claimed and is shown, for example, in the patent to Chase 1,768,509, June 24, 1930.

It has heretofore been proposed to use a link articulating a brake shoe to a rigid plate, but it is the belief of applicant that he is the first to secure fulladvantage of such an articulating anchorage. To the best of his knowledge he .is the first to associate with such an anchorage a ioating cam or its equivalent whereby the applied pressure may be equalized between the two shoes. To thatl end his cam 11 is carried by a link 22 which swings about a pivot 21, the swinging of which is intended to permit the equal division of the applied pressure between the two shoes. The swinging is resisted by a spring or springs such at 28. This resisting spring serves to restore the cam to its neutral posil tion subsequently to the brake application, adjustment of that lneutral position being effected by any convenient means, as `tor example by a plate 25 having parts 26 engaging the springs 23 and held fast by an adjustable securing member 27. This centralizing means is intended to be illustrative only and is not per se a part of this invention. The invention involves the centralizing means broadly in combination with other elements. By the use of the link 18 not only may the long shoe turn about its pivot 21, as it does in braking action, but it is free to turn about pivot 19. This latter pivotal connection is intended to function automatically at times to prevent the grabbing action of ybrake shoe 7 as for example when the coe'icient of friction of the lining rises considerably above -normal as from the iniuence of-heat. It also functions to render the self-actuatin force lmore eiiicient when the coeliicientof riction the cam does not have to overcome the swingcoeicient becomes high, a new and very desirable arrangement exists.

As stated above applicant is'not the first to use an articulating link for the anchorage .lof

of a brakev shoe. He nevertheless believes that he is the first to so locatel that link anchorage as to make possible the use of liningsfwith relatively high coefficients of friction, and to thereby lessen pedal pressure to .an extent not possible in constructions heretofore made. He also believes it to be novel with himself to so locate the anchorage that the point of maximum pressure along the arc of the shoe may automatically shift to prevent any danger of self-locking' when the coeiicient of friction increases and to prevent the brake becoming hard to operate if the coeiicient of friction decreases be- .low normal: It' should be explained that a shoe becomes hard to operate when the region of high pressure is near the-heel and a brake shoe tends to grab as the result of unduly high pressure near the toe or cam follower.

The brake shoe has an arcuate surface with a radius substantially the same as that of the drum. The brake shoe, however, turns about a point E (see diagrammatic view) and the movement, radially, lof the several points along the arc relative to the drum surace differs as the shoe swings. If a radius be drawn at right angles to the diameter through the shoe anchor E the point on the shoe in this radius (see radial line OA) has the maximum movement in the application and in the release of the shoe. Since there is a lesser movement in the case of points on the shoe arc in both directions from this 90 line, it will be seen that in releasing the shoe to provide clearance at the heel and toe there is a movement of the point in the 90 line more than nec-essary to effect its release. It will also be seen that by extending the shoe arc equally on each side of that 90 line the release movement of the shoe is minimized since under these circumstances the excess movement of the point in the 90 line is the same for both extreme positions. The desirability of minimizing release movement will be understood since all shoe movements are accomplished by pedal movements, and owing to the necessary leverage between the pedal and shoe all shoe movements are present to a multiplied extent at the pedal. To the same end- ,x avoiding undue pedal movement-the shorter the shoe the better, and therefore any struc'- drum.

tural arrangements which add to the eiciency of the brake and therefore make possible a lesser length of arc are advantageous in practice. It is therefore verydesirable that the middlepoint of the arc of the vshoe should be in the,90 line, or, if that'be impossible, .it should be' as near that line as may be.

It has been explained above that the middle l point of the arc should be in the 90 line. This point will then have the greatest movement as the shoe moves into contact with the When pressure is applied to produce frictional retardation since the greatest movement is in this 90 will be greatest. In the preferred arrangement, therefore, this mid point lying in the 90 line may be called the high pressure point of the shoe when the shoe is pressed into contact with the drum.

At this point in the discussion the several forces acting on the self-actuating shoe may well be considered. There4 is the cam-applied force acting on a line between the contact point. between the camand the end of the shoe or'rocker 29 which I prefer to use and the pivot point 31 between the rocker and the shoe. This force rotates the shoe about its pivot 21 (or pivot E as in the diagrammatic view). It rotates it counterclockwise into contact with the drum. As the E drum rotates, self-actuating frictional forces are set up uas the result of .drum rotation. The forces'at the several points of tangency have varying lever arms, the longest being those `of the forces adjacent the toe of the shoe. As a result,the tangential frictional force moments increase for such forces applied toward the toe of the shoe. Then there are the normal forces acting in a radial direction between the drum and the shoe.

It willbe evident not only that the frictional forces adjacent the toe have relatively long` lever arms, but that,.within the range of the contact region, the effective components of the frictional forces operating to rotate the shoe and acting at right angles to lines from the shoe pivot to tangency are relatively high. Alsoit will be seen that the proportion between the ef fective components and the frictional forces increases as the pivot point E approaches the center O. It is thcrefore 'to be desired that the point E be located asisnear the center` O as possible in order to render the frictional forces as effective as possible in supplementing the cam-applied force. Obviously, there is a limit since these forces may. become so -great as to lock the shoe to the drum. It has been found most advantageous to assume a theoretical locking coeiiicient of friction at whicha rigid. directly pivoted shoe will lock to the drum for a given length and location of shoe arc, which may be indicated by the angles B1 and B2 in the diagrammatic view and for such conditions to determine localine here valso the pressure lli) the points of p tion of the point E inl the case of a drum of given radius. This has been found to be poslsible by the use of the following formu a: l A l d, anchor pin distance,

g sin Ba) .r X locking coeilicient X A in2 BdB In this formula d is` the distance between the anchor pivot E and the drum center and r is the radlus of the drum, the angles B1 B2 being as shown in the diagram.

It has also beenfound that the locus of the intersection of the resultants of the nor'- mal and frictional forces is an arc concentric with the drum and of reater radius than the drum, the position of t 1e arc being dependent upon the radius of the drum and the angles B1 and B2 as before. The formula forA lov eating this arc is as follows:

v andB, the angles as in the diagram. An

In this formula CR represents the radius of the arc, r the radius of the circle and B1 whose vertexes lie in this arc, one of the sides of which pass through the center O may be constructed such that the angles have tangents'equal to assumed' coeiiicients of fric tion. In the case of an assumed normaler control coeilicient of friction the radial line OA, the 90? line described above, represents thefline through which the resultant of the normal forces acts and the other side represents the line through which the resultant of th'e normal forces and the frictional forces act. If therefore a normal or control. co-

eiiicient of friction be assumed such that-the resultant of all the normal forces passes through the 90 line, the line AL whose tangentcequals the assumed controlcoeici'entjof friction would be Vthe line through which the resultant of both normal and fr ictional forces operate.

. If then an actual locking coeicient be assumed for "an articulated shoe, that is a coeiiicient suchk as will cause the shoe to lock to the drum in the absence of any cam-operated force, it is possible to .construct an angle whose tangent is equal to the assumed actual locking coeicient, one side of the angle pass- I ing through the center of the circle and reprevSanting the resultant of all the normal forces then acting andthe other line representing A the resultant of both the normal and the frictional forces. It will be understood that this other line represents the condition where the normal and frictional forces are assumed to be great envough to lock the shoe to the drum convenient is selected a point B for the pivot -by the cam is to act. When no force 1s exlesv to rotate. This resultant with its lever arm tends to rotate the link about the point E from -cver the coefficient changes the eect ofsuch in the absence of pedal pressure. The diagrammatic view shows by lines OAL and by lines OKE these two conditions. This ligure -also shows-other angles having other tan- 7'0 gents, the conditions prevailing .withV other coeicients of friction. For convenience this arc representing the locus ofthe resultante may be called the origin point circle. In

the'li'ne KE at a point as far from E as is of the link I8 with the shoe 7.

Since this line KE represents the resultant of the normal land frictional forces which locks the shoe to the drum when no force is being applied by the cam, this line KE represents the ultimate resultant of all forces then operating, and therefore the point B being located in this resultant line there. is no tendency of the shoe to turn about point B. The lines KE andlAL extended' intersect at a point P through which the force applied ertedby the cam as explained in the self-l locking position of the parts the line PE represents the resultant of all the forces. In the case where the resultant' of the frictional and normal forces operates through the hne AL,

or better throigh the line PL there must be i a vforce applic by the cam in such' a direction as to cooperate with the resultant of the frictional and normal forces and to produce an ultimate resultant which shall ap lythe shoe tothe drum in such a way that t e normal forces are equally distributed about the 90 line. In other words the resultant of the normalJforces must be in the line OA, not OK,

as in the case of the self-locking shoe. The combinedresultant of the frictional and normal forces when acting through AL, together with the cam forces produce a combined resultant corresponding with which there is a link axis such as to equally distribute the normal forces about the radial line OA.

If the parts be assumed tobe in the self-A i locking position, and if the coeicient of friction becomes reduced from the self-locking coefficient to the control coefficient, the new forces will have a combined resultant which will have .a lever arm (such a lever arm will be the perpendicular droppedcenter E. to such resultant line) tendingto causethe link theposition it occupies `when self-locking, swinging point Btoward the c enter O, For every assumed coeilici'e'nt of friction there 1s anangular positionl of the shoe and link auch as to locate' the high pressure point at a particular position inthe arc of the shoe. Whenaction is to produce a c ange-in the relative intensities of the normal forces at the several points along .the arc of `the shoe. Y

The unavoidable deflections of the drum and changes 'in the shape of the shoe, due

`uted about the 90 radial line.

among other causes to changes in temperatur'e,permitv a turning of the link and a relatively changed position of the shoe and link.

-Such a turning is accompanied by a redistribution of the pressure points along the Y shoelwith a new position for thehigh pres-l *sure point. With an absolutely rigid drum 'and shoe not changeable in shape, there will be a tendency for the shoe to turn relative to the link but no actual change in relative position will take place. Such drums and shoes, however, do not exist, and in the absence of lthe-pivot at B to offset unavoidable drum de- 'iiection and shoe distortion, when such det iiection or distortion occurs, the action of the lshoe might be such as to cause it to lock to the drum or to become unduly hard to operate.

It will therefore be seen that when the resultantof the normal and frictional forces operate along the line AL, which makes with the line AO an angle whose tangent'is the assumed control coefficient, a condition will exist such that the forces are equally distrib- If the frictional coelicient changes a new distribution of the pressures betweenthe drum and v.the

Y shoe will take place as explained above,`the

high pressure point along the arc of the shoe moving either toward the heel or toward the vtoe away from the 90 line. It should be explained that preferably the line of action of the cam force should be determined to produce such a resultant with the line AL that' the normal forces may be equally distributed about the 90 line as explained above. Nevertheless in some constructions it may be more convenient to establish a cam line and compromise on the control coeicient of friction. -Variations also may be made in the assumed actual locking coeilicient.

. It is to be understoodthatin determining the point E a theoretical locking coeiicient was assumed as for a rigid shoe pivoted at E.

' -Such a shoe will lock with a coeilicient of `friction less than one which is anchored `by 'the link, since the latter causes the readjustment of pressures as explained above.- It will Vtherefore be understood that lin assuming an actual locking coeiicient for an articulated shoe a coefiicient higher than the assumed theoretical locking coeiicient for the "shoe made possible. The greater the difference between the assumed theoretical locking coeiiicient and the assumed actual locking vcoeilicient, the greater will be the correction fwhich may be had for changes in lining co- I etlicients .65 -line AL to produce a combined resultant Referring now to the diagram to make clear the operation ofthe novel brake, it will be understood from what has been said, that a force applied at the cam operating through the point P lcooperates with fricti nal and lnormal forces acting in the direction of the forces between the shoe and the drum shall be equal on each side of the 90 lineOA, with the high pressure point in that line. If now, with the brake so apglied, there should be an increase in the coe cient of friction, due perhaps to a temperature vchange, that increasel of' coelicient will cause changes in the shoe and drum which might result in selflocking. Owing, however, to such changes and to drum deflection and shoe'distortion rotation occurs not only about pivot E but about pivot B' whereby thelink line corresponds with the new resultant of forces. A new adjustment will take place which will cause the link to move about pivot E tending to swing the point B away from the center of 'the drum toward the-drum flange, this swingingv being accompanied by a rotation about point B as a result of which a line CA2 will represent the resultant of the norrrlilal forces acting between the drum and the -s oe.

This brings the highpressure point away from the 90 line 'to a point nearer-the heel of the shoe. There is therefore an automatic correction. When the coefficient of friction rises and tends to render the friction effects greater, the point of high pressure simultaneously shifts to a region of the shoe nearer the heel so as to minimize the effects of the higher coefficient, and to that extent reduce the danger of self-locking.

In a similar way, should the, frictional forces become less, the link tends to shift with an opposite direction of rotation and "of the shoe to the drum.

When the brake is released the long shoe should rotate about its anchor pin center E and not about the pivot B. l To insure this action suitable frictional retarding means.

should be provided between the shoe and the link. To that end the shoe may be provided with an aperture at its heel in which may be seated a spring 37 having at its ends abutments 39 engaging the two parts of the articulating link. A

The pull of the retracting spring on the long shoe should be so arranged that it;` does not tend to pull the shoe toward the toe en' toward theheel Iwhen the shoe is in the released position. This is accomplished byl having the center line of the Aretractive spring ass through the intersection P of the Acam orce line and the link line as indicated by dot and dash line in Fig. 2. If 4for any reason the center line of the spring must pass outside the point Pthe discrepanc should be taken care of by increasing the rictional drag between the shoe and the links at the heel end of the shoe.

When the vehicle is moving backward and the brakes are applied, the long shoe becomes the non-self-actuating shoe, and the resultant of the normal and frictional forces crosses the arc of the lining surface on that side of the 90 line .toward the toe end of the shoe. It-

is possible that this intersection may fall ahead of the 'toe of the shoe, -a condition to be avoided as it will cause a shifting of the shoe when the brakes are applied during the n backward motion of the car after having been applied during forward motion of the. car. On the diagrammatic view a line PD has been drawn through the end of the lining.V

From C theintersection of PD with the origin point circle a line.CO is drawn to the center of the brake. The angle OCD to avoid the shifting' action mentioned above lshould be one whose tangent is at least as large as the highest coeflicient ci `friction to be encountered. If this precautlon is made there is no danger of the frictional and normal forces swinging the long shoe when it becomes. non-sel ctuatin l In the case of the short slice the location of its'v pivot may be determined by the method indlcated for locatin the pivot E in the case of the long shoe. AO viously this int will be at a dlierent .distance from t e center since the arc of the shoe is dierentl posie long shoe.V Inasmuch as the short shoe functions chieii in the case of reverse driving it has `been ound unnecessary to resort to the refinements of the articulated link used in the case of the long shoe.

Should 1t be found inconvenient to locate the long shoe symmetrically with reference to the line a correction corresponding to the discrepancy should be made in locating the ori 'n point circle. A

y the above provisions it will be seen that maximum eiiiciency is obtained by the'use of shoes arranged to best advantage within the brake drum and that the shoes occu y such a part of the drum as to leave rqom or an additional or an emergency brake within the same drum. l Owin to the use of the articulating link it has .en seen that it is possible to use linings of higher coefficients than heretofore without danger of self-locking, this result being accomplished by the shlfting of the high pressure points of the shoe to and from the medial line. All the advantages of such an arrangement of shoes are supplemented by the use of the floating cam to divide the applied pressure equall between the self-actuating and the non-sel actuating shoe. In practice considerable latitude is possible in the assumption of such factors as the control coetlicient, that being the coeilicient of Vfriction in the' case where the resultant of the drum reaction forces lies in the 90 line'; in. the assumed theoretical locking coeiiicient which was used to determine the best location for point E; this bein the locking coeilicient for a rigid shoe pivote at E, and inthe assumed actual locking coeiiicient which was used t determine the position of the link relative to the shoe when drum, a ixedsuppor't, la. link pivoted to one 'of said shoes and to said su port,the axis of `said link being such that t e hi h pressure point along the arc of the shoe 'es in that vdrum radius which is at right angles to a diameter through the pivot between the link and the suport for a predetermined assumed control dcox,1 cient of riction levleen the liningan te rum, oatin r ea lying' means to spread adjacent ginds of said) shoes into contact with saidw drum. l

2. In a brake, a drum, shoes to engage the drum, a .fixed su'pport, floatingA means between adjacent ends of said shoes-to spread said shoes into drum engagement means pivotall connecting one of said shoes to the fixe support, means affording a link articulation between the other shoe and the fixed support, said link articulation means having' .an axls such that the high pressure oint along 4the arc of the shoeA lies in that rum radius which is at right angles to a diameter throughjthe pivot between the link and the support for a E11-determined assumed control eiclent of 'ction between the lining and e drum.

3. In a'brake, a drum, a pair of shoes, means. to s read said shoes into frictional 'contact wit said drum, a fixed support, means to directly pivot one of said shoes to the fixed support, a link pivoted tothe other shoe and to the fixed support, the axis of said link being such that the high pressure point alongvthe arc of the shoe lies in'l that drum radius which 4is at right angles to a diameter through the pivot between the'link and the .y ksupport for a predetermined assumed. control coeicient of friction between the liningf125 Y 4. The invention defined by claim r3, the

and the drum.

link articulated shoe havingialonger arc of contact with the oted shoe. 1 1 y 5. In' a brake, a drum, a lixed support, a

than the directly pij- U the shoe self-locking for an assumed theoretical coefficient ofI friction .between the drumandk the shoe. v

6. In a brake, a drum, a shoe, a fixed support, means to move said shoe into frictional contact with said drum, a link pivoted to said` shoe and to said support, the link being v mechanical means-to rotate said shoe solely angular relai-,ion of said shoe movable-about its pivot with the support, its axis coinciding with the combined resultant of the `frictional self-actuating force produced by the rotating drum upon the shoe and the normal forces between the drum and the shoe for an assumed actual locking vco eiicient of friction between the shoe and the drum.

7. In a brake, a rotatable drum, a. fixed support, a shoe, means to move said shoe into frlctional contact withsaid drum, a link pivoted to said shoe and to said support, said link coinciding with the resultant line of the several forces operating upon said shoe whereby the high pressure region of the arc of the shoe may move along the arc and is so positioned for an assumed normal or control coeiicient of friction between the shoe and the drum that the high pressure point of the shoe lies substantially in the drum radius at right angles to a diameter through the pivot between the link and the fixed plate.

8. Ina brake, a rotwably mounted drum, a fixed support, a shoe having a linin ,means to move said shoe into contact with said drum, a link pivoted to. said shoe and to said support, said link being movable about its pivot with the support, whereby said shoe is moved into contact with said drum, the axis of said link being such that the high pressure point along the arc of the shoe lies in that drum radius which is at right angles to a diameter through the pivot between the link and the sup grt for a giredetermined assumed control coe cient of riction between the lining and the drum. I

9. In a brake, a drum, a fixed support, a shoe havinga lining to engage the drum, a link pivoted to said shoe and to said support,

about the pivot between the link and the support and into contact with the drum, the axis of. said link when the shoeis so en- 4 gaged with the drumcoinciding with the resultant of all the forces acting upon said shoe,

and said axis being shiftable with changes in' the -coeiiicient of frictionfrom an .assumed normal or control coeicient in such a way that, for the control coefiicient, the high pressure point of the shoe. is in the radius at right angles rto the diameter through the link point when the coeiiicient changes.

an assumed control lining coefiicient of friction the high pressure point of said lining lies in that drum radiusv at right angles to the d1- ameter through .the pivot between the link and the support. l

11. In a brake, a rotatable drum, a fixed support, a shoe, a link pivoted to said shoe and to said support, means including an'element for applying mechanical force to sald shoe, said mechanical force being su plemented by a self-actuating frictional orce, said forces acting to rotate said shoe into drum contact solely about the pivot'between the link and the support for an assumed control coeiiicient of friction between the shoe and the drum, and also tending to rotate said shoe about the pivot point. between the shoe and link as the frictional coefficient changes from the assumed control coeiiicient, whereby the high pressure point of the shoe is normally in the drum radius at right angles to a diameter through the pivot between the link and the support but which high pressure point moves therefrom to increase the effective action of the frictional self-actuating force `when the coeflicient decreases and to lessen the effective action of said frictional self-actuatin force when the coelicient of friction rises aove the assumed normal or control coeliicient.

12. In a brake, a rotatable drum, a shoe, a fixed support, a first and second pivot anchorage between said shoe and said support, mechanical means to move said shoe into contact with the drum the rotating 'drum serving as a self-actuatmg force to similarly rotatesaid shoe, said forces acting' about the first of said pivots only for any one coeiiicient of friction but about the lirst and second pivots when the coeicient of friction isA changing to thereby effect a change in the high pressure point of said shoe.`

13. r1he invention defined by claim 12, the to its anchorage for an assumed control coefficient being such that the high pressure'point-of the shoe lies in that drum radius which is at right angles to the diameter through the first plvot.

14. In a brake, a.v drum, a shoe, a fixed support, mechanical means to move said shoe into contact with said drum, a link pivoted to said support and to said shoe at a point between its mid point and its heel, means to rotate -`said lshoe together with saidlink as a unit about the pivot between the link and the support, sai'd yshoe being rotatable about its pivotal connection with 'the link solely under the inioof iuence of changes in v tion between the shoe and the drum and drum and shoe changes to thereby shift the high pressure point along the are of the shoe. y

15. The invention defined by claim 14, to-

l gether with a shoe-releasing spring attached to said shoe and having its axis intersecting the point of intersection of the manually ilied force and the longitudinal axis of the Iii testimony whereof I affix e 'LOU my signature.

S C. HUCK.

the coeieient of fric? 

